JP7030820B2 - Method for producing hydrogen cyanide - Google Patents

Description

The present invention relates to a method for producing hydrogen cyanide by reacting ammonia with methane, which allows the production unit to operate at a nominal capacity for hydrogen cyanide for a longer period of time.

Background of the Invention In the so - called BMA process for producing hydrogen cyanide on an industrial scale ( Blasauure aus Methane and Ammoniak ), a feed mixture containing ammonia and methane contains platinum. By reacting on a catalyst at a reaction temperature of 1000 ° C. to 1400 ° C. in a heat absorption reaction, a product gas mixture containing hydrogen cyanide and hydrogen is obtained. In an industrial plant for producing hydrogen cyanide by the BMA process, the feed mixture is conducted into a reaction tube of aluminum oxide whose inner surface is coated with a platinum catalyst, and these reaction tubes are gas-heated reactions. They are arranged in parallel in the furnace.

At the high temperatures used in the BMA process, methane and other hydrocarbons contained in the feed mixture can be decomposed into carbon and hydrogen, and ammonia can be decomposed into nitrogen and hydrogen. Therefore, the BMA process is usually carried out with incomplete methane conversion using a molar excess of ammonia, thus resulting in a product gas mixture containing unreacted ammonia and unreacted methane, in which ammonia. The concentration is higher than the methane concentration. Ammonia to carbon molar ratios in the range 1.01: 1 to 1.30: 1 in the feed mixture have been reported in the literature. F. Ender, Chemie-Ing. -Techn. 30 (1958) 305-310 had 71.8% by volume hydrogen and 22.9% by volume of hydrogen cyanide by operating an industrial plant at a molar ratio of ammonia to carbon of 1.05: 1 in the feed mixture. , 2.5% by volume ammonia, 1.7% by volume of methane, and 1.1% by volume of nitrogen-containing product gas mixture is disclosed.

German Patent Application Publication No. 2947498 (DE2947498A1) discloses that unreacted ammonia from the product gas mixture of the BMA process is recovered by desorption following absorption on zeolite. A product gas mixture containing 22% to 25% HCN, 2% to 5% NH ₃ , 70% to 75% H ₂ , and trace amounts of water, CH ₄ , and N ₂ is disclosed as an example. At that time, the BMA process is carried out in a research furnace containing a single reaction tube.

Decomposition of methane and other hydrocarbons during the BMA process can result in the formation of carbon deposits on the inner surface of the reaction tube, resulting in blockage of the reaction tube. Since aluminum oxide is brittle, aluminum oxide reaction tubes can also be damaged during operation. Operation of the reactor may be continued by shutting off the gas supply to the reaction tube if the reaction tube is blocked or damaged. However, maintaining the desired production rate of hydrogen cyanide requires increasing the rate of supply to the remaining reaction tubes, increasing the reaction temperature, and achieving sufficient conversion at the increased supply rate. This can only be done up to a certain limit, and the reactor will be shut down to replace the blocked or damaged reaction tube if the number of outaged reaction tubes exceeds a certain limit. There is a need to. The cooling of the reactor and the reheating to the reaction temperature required to replace the reactor tube puts mechanical stress on the reactor material and reduces the operating time of the reactor. Shutdown of the reactor also temporarily reduces the output of the hydrogen cyanide production plant. Therefore, it is required to operate the reactor in the BMA process for as long as possible.

German Patent Application Publication No. 242116 (DE242116) reacts by temporarily conducting a carbon dioxide stream through the reaction tube when the pressure drop along the reaction tube increases by 25% to 45%. It teaches that a longer operating period can be achieved for the BMA process by regularly removing the carbon deposits that form inside the pipe. German Patent Application Publication No. 242116 (DE242116) further proposes additional ammonia treatment at intervals of 3-7 days, 1.05-1 to which is used in normal operation. The molar ratio of ammonia to carbon of .075 is temporarily increased from 1.20 to 1.30 over a period not exceeding 20 minutes. German Patent Application Publication No. 242116 (DE242116) also sets the ammonia content in the feed mixture to 0.5 more than the methane concentration in the product gas mixture for reactors accommodating reaction tubes of various ages. It is suggested that the concentration of ammonia in the product gas mixture should be adjusted to be 100% to 1% by volume higher. German Patent Application Publication No. 242116 (DE242116) teaches in this regard that such slightly increased ammonia content does not damage the catalyst.

Summary of the Invention Here, the ammonia concentration in the product gas mixture and the methane concentration in the product gas mixture are the periods during which the reactor can be operated until it becomes necessary to replace the blocked or damaged reaction tube in the BMA process. Preceding that this concentration difference is maintained in the range of 0.5% by volume to 1% by volume by performing the process while maintaining a concentration difference between and above 1% by volume for most of the time. It turns out that it can be significantly extended compared to the method of technology.

Accordingly, the subject of the present invention comprises conducting a feed mixture containing ammonia and methane into a reaction tube whose inner surface is coated with a catalyst containing platinum at a reaction temperature of 1000 ° C to 1400 ° C, thus hydrogen cyanide. A method for producing hydrogen cyanide, which provides a product gas mixture containing hydrogen, unreacted ammonia, and unreacted methane, wherein the ammonia concentration in the product gas mixture is higher than the methane concentration in the product gas mixture. Also high, here the concentration difference between the ammonia concentration and the methane concentration over a period of at least 100 hours, the adjustment of the reaction temperature over at least 80% of the time, the ammonia vs. carbon in the feed mixture. A method of maintaining in the range of 1.05% by volume to 3.0% by volume by adjusting the molar ratio, adjusting the supply rate of the feed mixture, or any combination of said adjustments.

Detailed Description of the Invention In the method of the invention for the production of hydrogen cyanide, a feed mixture containing ammonia and methane is conducted in a reaction tube whose inner surface is coated with a catalyst containing platinum. The reaction of ammonia with methane is carried out at a reaction temperature of 1000 ° C to 1400 ° C, thus resulting in a product gas mixture containing hydrogen cyanide, hydrogen, unreacted ammonia and unreacted methane.

The feed mixture preferably contains ammonia and methane as main components, and may further contain hydrocarbons such as ethane or propane in addition to methane. However, the content of hydrocarbons other than methane is preferably kept low, with methane preferably forming at least 90% by volume, more preferably at least 98% by volume of the hydrocarbons contained in the gaseous feed mixture. The use of feed mixtures with low content of hydrocarbons other than methane reduces the formation of carbon deposits in the reaction tube caused by the thermal decomposition of higher grade hydrocarbons.

The total amount of ammonia and methane in the feed mixture is preferably at least 90% by volume, more preferably at least 98% by volume. The feed mixture preferably has a low content of oxygen, preferably less than 4% by volume, more preferably less than 1% by volume. The feed mixture is preferably prepared by mixing natural gas with gaseous ammonia. Preferably, natural gas is used that has been purified from the natural gas supply network from which carbon dioxide and sulfur compounds have been removed. The feed mixture preferably contains a slight molar excess of ammonia relative to methane and other hydrocarbons, 1.01: 1 to 1.30: 1, preferably 1.05: 1 to 1.16: 1. Included in the molar ratio of ammonia to carbon. The use of molar excess ammonia allows for high conversion of methane and reduces the formation of carbon deposits in the reaction tube caused by the thermal decomposition of methane.

The reaction between ammonia and methane is carried out by conducting a feed mixture in a reaction tube whose inner surface is coated with a catalyst in the presence of a catalyst containing platinum metal at a reaction temperature of 1000 ° C to 1400 ° C. The reaction of converting methane and ammonia to hydrogen cyanide and hydrogen is an endothermic reaction and the required reaction temperature is generally provided by external heating of the reaction tube. The reaction is preferably carried out in a reaction furnace preferably containing 10 to 130 reaction tubes operated in parallel, wherein the reaction tubes are preferably natural gas or natural gas and hydrogen. It is heated by combustion gas from a gas burner that uses the mixture as fuel. Each reactor preferably has a supply conduit for distributing the feed mixture to the reactor reaction tube and a product conduit for recovering the product gas mixture formed in the reactor reaction tube. Suitable reactors include prior art such as German Patent Application Publication No. 1041476 (DE1041476), European Patent Application Publication No. 0074504 (EP0074504A1), and European Patent Application Publication No. 0125395A2. Is known from.

The reaction tube is preferably made of a heat resistant ceramic material such as aluminum oxide or silicon carbide, and is preferably made of airtight sintered aluminum oxide. Suitable cylindrical aluminum oxide tubes with a length of about 2 m and an inner diameter of about 2 cm are commercially available. The reaction tube is known from the prior art, for example, European Patent Application Publication No. 0299175 (EP0299175A1), European Patent Application Publication No. 04077809 (EP0407809A1), and European Patent Application Publication No. 0803470 (EP0803470A1). Can be coated with a platinum catalyst using the method of. The reaction tube is used to improve heat transfer to the feed mixture in German Patent Application Publication No. 10785554 (DE10785554), International Publication No. 2006/050781 (WO2006 / 050781A2), and International Publication No. 2015 /. It may include internal attachments as described in 052066 (WO2015 / 052066A1) or ribs on the inner surface as described in WO 2014/198502 (WO2014 / 198502A1).

The reaction of ammonia with methane gives a product gas mixture containing hydrogen cyanide, hydrogen, unreacted ammonia, and unreacted methane. The ammonia concentration in the product gas mixture is generally higher than the methane concentration, and the ammonia concentration higher than the methane concentration makes the molar ratio of ammonia to carbon in the feed mixture 1.01: 1 to 1. It can be easily achieved by adjusting within the range of 30: 1. The product gas mixture may also contain nitrogen formed by the decomposition of ammonia into nitrogen and hydrogen.

The method of the present invention is intended to operate the reaction tube used to produce hydrogen cyanide for as long as possible when producing hydrogen cyanide in nominal capacity. This maintains the ammonia concentration in the product gas mixture 1.05% by volume to 3.0% by volume higher than the methane concentration in the product gas mixture over at least 80% of the time by adjusting the reaction conditions. Achieved by doing. The concentration difference between the ammonia concentration and the methane concentration is preferably 1.1% by volume to 2.5% by volume. The concentration difference between the ammonia concentration and the methane concentration can be an adjustment of the reaction temperature, an adjustment of the molar ratio of ammonia to carbon in the feed mixture, an adjustment of the feed rate of the feed mixture, or any of these measures. Depending on the combination, it can be maintained within the above range. An increase in the reaction temperature causes a decrease in the concentration difference, and a decrease in the reaction temperature causes an increase in the concentration difference. An increase in the molar ratio of ammonia to carbon in the feed mixture will result in an increase in the concentration difference, and a decrease in the molar ratio of ammonia to carbon in the feed mixture will result in a decrease in the concentration difference. An increase in the supply rate of the feed mixture will result in an increase in the concentration difference, and a decrease in the supply rate of the supply mixture will result in a decrease in the concentration difference. Preferably, the molar ratio of ammonia to carbon in the feed mixture is kept constant and the concentration difference is maintained by adjusting the reaction temperature. When the reaction temperature, the molar ratio of ammonia to carbon in the feed mixture, and the feed rate of the feed mixture are kept constant, the concentration difference between the ammonia concentration and the methane concentration in the product gas mixture is of time. It will change over time as a result of catalyst deterioration. Therefore, maintaining a constant concentration difference generally requires adjusting the working conditions over time.

The operating conditions are generally such that high conversions of methane and other hydrocarbons contained in the feed mixture are obtained, preferably less than 4% by volume of methane concentration in the product gas mixture. Be adjusted.

The advantage of the method described in the claims is that the concentration difference between the ammonia concentration and the methane concentration is in the range of 1.05% by volume to 3.0% by volume over a sufficiently long period of at least 100 hours. Achieved by maintaining in. The period can be 100 to 100,000 hours, preferably 4000 to 40,000 hours. The period preferably includes the total operating time of the reactor, excluding the catalyst conditioning step at the first start of the reaction tube, which typically takes 15-60 hours. The concentration difference need not be in the range of 1.05% by volume to 3.0% by volume over the entire period, but may be lower over 20% or less of that period. The concentration difference should not be higher than 3.0% by volume over any extended period. Preferably, for a period of at least 100 hours, the concentration difference is 3.0% by volume or less over at least 95% of that time, preferably at least 98% of that time.

The increased concentration difference is, for example, the implementation of the method for preventing soot deposits in the reaction tube described in page 4, lines 25-36 of German Patent Application Publication No. 242166 (DE242116A1). May be acceptable for a short period of time. For this purpose, it is preferred to increase the molar ratio of ammonia to carbon in the feed mixture by 10% to 30% over a period of 30 minutes or less at time intervals of 15 to 300 hours.

In a preferred embodiment, the concentration difference is maintained at a constant value in the range of 1.1% by volume to 2.1% by volume over at least 95% of the time. Keeping a constant concentration difference within this narrow range over at least 95% of the time is particularly effective in preventing blockage or breakage of the reaction tube.

1.1 Compared to prior art methods operated with concentration differences of less than% by volume, the methods of the invention not only allow longer operating times of the reactor, but also for hydrogen cyanide at lower reaction temperatures. The same output rate is also achievable, thereby increasing the life of the reactor and reducing the heat loss that occurs during heating of the reaction vessel, thus reducing the energy consumption of the method.

The method of the present invention is operated in parallel at a constant hydrogen cyanide production rate, and the loss of production capacity caused by blockage or breakage of the reaction tube is compensated by increasing the supply rate to the remaining reaction tubes. It is particularly advantageous for producing hydrogen cyanide using a reaction tube. Such an increase in the rate of supply to the individual reaction tubes over operating hours will result in a decrease in the yield of hydrogen cyanide. Therefore, the calculated yield of hydrogen cyanide for the supplied ammonia is initially small compared to the prior art method operated with a concentration difference of less than 1.1% by volume in the case of the method of the invention. Although lower, the average yield to ammonia over the entire operating time is higher for the method of the invention, which is surprising for methods operated at higher concentrations of unconverted ammonia.

The concentrations of ammonia and methane in the product gas mixture can be measured by conventional methods for gas analysis. For example, the concentration of ammonia can be measured by absorbing ammonia in a solution containing a known amount of acid and titrating the unconsumed acid. Methane can be measured by GC analysis after absorption of ammonia and hydrogen cyanide from the product gas in acidic and alkaline aqueous solutions. Preferably, the concentrations of ammonia and methane in the product gas mixture are measured simultaneously by infrared spectroscopy or gas chromatography. Infrared analysis of the product gas mixture can be performed on the basis of infrared absorption of ammonia at 1718 cm ^-1 and infrared absorption of methane at 2940 cm ^-1 and calibration with a mixture of known compositions. Infrared analysis is preferably performed using an FT-IR spectroscope. GC analysis of the product gas mixture is preferably performed using a sample splitter with different columns for methane and ammonia analysis. Methane is preferably analyzed on a molecular sieve-filled column and ammonia is preferably analyzed on a capillary column, eg, a PoraPLOT Q column manufactured by Agilent J & W.

The method of the present invention is preferably carried out in a plant equipped with one or more reactors and at least two reactors in which each reactor is operated in parallel. Each reactor contains 10 to 130 reaction tubes operated in parallel. Preferably, the reactor described further above is used. Each reactor in the plant comprises a reactor product conduit for recovering the product gas mixture of the reactor in the reactor. The plant preferably comprises 1 to 30 reactors, more preferably 2 to 15 reactors, wherein each reactor has 2 to 20 reactors, preferably 8 reactors. It is equipped with 16 to 16 reactors.

Ammonia and methane concentrations are analyzed in the combined product gas mixture from a single reactor, the combined product gas mixture in the reactor product conduit, or both product gas mixtures, and thus the reactor. Alternatively, the concentration difference for all reactors can be measured. Preferably, the concentrations of ammonia and methane in the product gas mixture are measured simultaneously by infrared spectroscopy or gas chromatography.

Preferably, the operating conditions are such that for each reactor in the plant, the concentration difference in the combined product gas mixture from the reactor is maintained within the range of 1.05% by volume to 3.0% by volume. It is adjusted to be. That is, for each reactor, the concentration difference is maintained in the combined product gas mixture from the reactor. Multiple reactors of the reactor may be operated with different concentration differences within the above range. Similarly, the reactor of the plant can be operated with various concentration differences within the above range. Preferably, each reactor in the plant is operated with the same concentration difference, more preferably each reactor is operated with the same concentration difference.

If the reaction tube is blocked or damaged, the supply of the feed mixture to this reaction tube is preferably stopped and the reactor containing the thus blocked or damaged reaction tube is further operated by the remaining reaction tubes. Is possible. The rate at which the feed mixture is supplied to the reactor containing the blocked or damaged reaction tube can be increased to maintain a constant production rate for hydrogen cyanide. Preferably, the rate at which the feed mixture is fed to the reactor, including the closed or broken reactor, is kept essentially constant, which is the other of the reactor with the same feed to the closed or broken reactor. It has the effect of not only being transferred to the reaction tube, but also to other reactors of the reactor. Preferably, the reaction temperature of one or more reactors to which the blockaged or damaged reactor tube feed is transferred is increased so that a constant concentration difference is maintained for the reactor or reactor.

In order to prevent blockage of the reaction tube by carbon deposits, it is preferable that one or more reaction tubes of the reactor are further heated while conducting carbon dioxide through one or more reaction tubes of the reactor. Can be temporarily shut down to remove carbon deposits by applying the method described in Japanese Patent Application Publication No. 242166 (DE242116A1).

Example 1 (Comparative Example)
A cylindrical reaction tube composed of sintered aluminum oxide having a length of 2100 mm and an inner diameter of 17 mm is coated with a platinum-containing catalyst and is described in Example 6 of Japanese Patent Application Publication No. 0407789 (EP04078709A). Was activated. A stream of feed gas composed of 28.0 mol / h ammonia with a molar ratio of ammonia to carbon of 1.10 and 25.5 mol / h methane was then heated vertically in a research furnace to 1240 ° C. It was conducted from below in the reaction tube facing. The product gas mixture coming out of the reaction tube was analyzed. The yield of hydrogen cyanide was 87.8% based on ammonia and 96.6% based on methane.

Example 2
Example 1 was repeated using a feed gas stream composed of 36.0 mol / h ammonia and 32.7 mol / h methane having the same ammonia to carbon molar ratio of 1.10 as in Example 1. The yield of hydrogen cyanide was 83.8% based on ammonia and 92.1% based on methane.

Example 3
A prior experiment for producing hydrogen cyanide in a reaction tube prepared as in Example 1 under operating conditions where the concentration difference between the ammonia concentration and the methane concentration in the product gas mixture is less than 1% by volume. A reaction tube that had been used for over 150 hours was used. A stream of feed gas composed of 28.0 mol / h ammonia with a molar ratio of ammonia to carbon of 1.14 and 24.6 mol / h methane was then heated vertically in a research furnace to 1330 ° C. It was conducted from below in the reaction tube facing. The product gas mixture coming out of the reaction tube was analyzed after reaching steady state. The temperature of the research furnace was then lowered to 1180 ° C. in steps of 30 ° C. and waited until steady state was reached each time before analysis of the product gas mixture. Table 1 was burned for the concentrations of ammonia and methane in the product gas mixture, the concentration differences, the yields of ammonia-based and methane-based hydrogen cyanide, and the amount of hydrogen cyanide produced and the heating of the research furnace. Shows the energy consumption calculated from the amount of gas.

Table 1

Example 4 (comparative example)
Ammonia vs. carbon reactors in a production plant equipped with 10 reactors of the design described in European Patent Application Publication No. 0125395 (EP0125395A2), each containing 26 reaction tubes. It was operated with a feed mixture of methane and ammonia having a molar ratio of 1.09. The feed stream was adjusted to maintain a hydrogen cyanide output of about 179 kg / h and the reactor temperature was adjusted so that the concentration difference between the ammonia concentration and the methane concentration in the product gas mixture was about 0.5% by volume. Adjusted to be maintained. Concentrations of ammonia and methane were measured by infrared spectroscopic analysis and GC analysis in the reactor product conduit. To prevent the formation of carbon deposits in the reaction tube, the molar ratio of ammonia to carbon in the feed mixture was temporarily increased by 20% over a 15 minute period at 2-day intervals. As a further measure, carbon dioxide was conducted in the reaction tube at intervals of approximately 28 days according to the procedure described in German Patent Application Publication No. 242166 (DE242116A1). Table 2 shows the HCN yield, the number of blocked or damaged reactor tubes, the average load per reactor tube used, and the average reactor temperature over a run time of 19200 hours.

Table 2

Example 5
Example 4 is repeated using a natural gas with a molar ratio of ammonia to carbon of 1.10 and a feed mixture of ammonia, and the reactor temperature is determined by the concentration difference between the ammonia concentration and the methane concentration in the product gas mixture. It was adjusted to be maintained at about 1.3% by volume. The formation of carbon deposits in the reaction tube occurred more slowly than in Example 4, so the molar ratio of ammonia to carbon in the feed mixture was temporarily increased at 5-day intervals and carbon dioxide was reduced. Conduction was carried out in the reaction tube at intervals of 3 to 4 months. Table 3 shows the results.

Table 3

Claims (16)

The feed mixture containing ammonia and methane comprises conducting at a reaction temperature of 1000 ° C to 1400 ° C in a reaction tube whose inner surface is coated with a catalyst containing platinum, thus hydrogen cyanide, hydrogen, unreacted ammonia, and the like. And a method for producing hydrogen cyanide to obtain a product gas mixture containing unreacted methane, wherein the ammonia concentration in the product gas mixture is higher than the methane concentration in the product gas mixture, where at least 100. Over a period of time, the concentration difference between the ammonia concentration and the methane concentration, over at least 80% of the time, adjusting the reaction temperature, adjusting the molar ratio of ammonia to carbon in the feed mixture, said feed. A method of adjusting the feed rate of a mixture, or keeping it in the range of 1.05% by volume to 3.0% by volume by any combination of said adjustments. The method of claim 1, wherein the concentration difference during the period is 3.0% by volume or less over at least 95 % of the time. The method of claim 1 or 2, wherein the concentration difference is maintained at a constant value in the range of 1.1% by volume to 2.1% by volume over at least 95% of the time. The method according to any one of claims 1 to 3, wherein the total amount of ammonia and methane in the feed mixture is at least 90 % by volume. The method according to any one of claims 1 to 4, wherein the feed mixture contains less than 4% by volume of oxygen. The method according to any one of claims 1 to 5, wherein the molar ratio of ammonia to carbon in the feed mixture is kept constant, and the concentration difference is maintained by adjusting the reaction temperature. The method according to any one of claims 1 to 6, wherein the methane concentration in the product gas mixture is less than 4% by volume. 13. the method of. One or more reactors, each with at least two reactors operating in parallel, and a reactor product conduit for recovering the product gas mixture of the reactors, each reactor in parallel. The method according to any one of claims 1 to 8, wherein a plant including 10 to 130 reactor tubes to be operated is used. The ammonia concentration and the methane concentration are measured by infrared spectroscopic analysis in the combined product gas mixture from a single reactor, the combined product gas mixture in the reactor product conduit, or both. The method according to claim 9. The ammonia concentration and the methane concentration are measured by gas chromatography in a combined product gas mixture from a single reactor, a combined product gas mixture in a reactor product conduit, or both. Item 9. The method according to item 9. The method according to any one of claims 9 to 11, wherein for each reactor, the concentration difference is maintained in the combined product gas mixture from the reactor. The supply of the feed mixture to the reaction tube is stopped if the reaction tube is blocked or damaged, and the feed rate of the feed mixture to the reactor containing the blocked or damaged reaction tube, or the blockage or breakage. The method of any one of claims 9-12, wherein the feed rate of the feed mixture to the reactor containing the reaction tube is increased so that a constant production rate for hydrogen cyanide is maintained. The reaction tube or the reactor is temporarily shut down in order to remove carbon deposits by conducting carbon dioxide in the reaction tube or the reaction vessel of the reactor, according to claims 9 to 13. The method according to any one of the items. The method according to any one of claims 9 to 14, wherein the plant comprises 1 to 30 reactors, and each reactor comprises 2 to 20 reactors. The method according to any one of claims 1 to 15, wherein the concentration difference is maintained over a period of 100 to 100,000 hours.